In-situ crystallized zeolite containing composition (LAI-ISC)

ABSTRACT

Applicant has discovered a new zeolite containing composition and a process for preparing the same. The composition is unique in that the zeolite crystals making up one layer of the composition pack in a manner such that the composition is essentially continuous with no large scale voids even when the zeolite layer is &lt;10 μm thick. Thus, the present invention is directed toward a composition comprised of a porous substrate and a layer of zeolite crystals wherein said layer of zeolite crystals is a polycrystalline layer with at least 99% of said zeolite crystals having at least one point between adjacent crystals that is ≦20 Å and wherein at least 90% of said crystals have widths of from about 0.2 to about 100 microns (preferably about 2 to about 50 microns) and wherein at least 75% of said crystals have a thickness of within 20% of the average crystal thickness. Preferably the composition has at most 1 Volume % voids in the zeolite layer. Use of the composition is also described.

This is a divisional of Ser. No. 08/499,719, filed Jul. 7, 1995, nowU.S. Pat. No. 5,763,347, and a continuation-in-part of U.S. Ser. No.08/483,343, filed Jun. 7, 1995, now abandoned, which is aContinuation-in-Part of U.S. Ser. No. 267,760 filed Jul. 8, 1994, nowabandoned.

FIELD OF THE INVENTION

The present invention is related to a new zeolite containingcomposition, its preparation, and use.

BACKGROUND OF THE INVENTION

U.S. Pat. No. 5,110,478 describes the direct synthesis of zeolitemembranes. The membranes produced in accordance with the teachings ofU.S. Pat. No. 5,110,478 were discussed in "Synthesis andCharacterization of a Pure Zeolite Membrane," J. G. Tsikoyiannis and W.Haag, Zeolites (VOl. 12, p. 126., 1992). Such membranes are freestanding and are not affixed or attached as layers to any supports.Furthermore, the membranes have a gradient of crystal sizes across thethickness of the membrane. Such a gradient precludes growth of a thinmembrane with a minimum number of nonselective permeation paths.

Zeolite membranes have also been grown on supports. See e.g. "Hightemperature stainless steel supported zeolite (MFI) membranes:Preparation, Module, Construction and Permeation Experiments," E. R.Geus, H. vanBekkum, J. A. Moulyin, Microporous Materials, Vol. 1, p.137, 1993; Netherlands Patent Application 91011048; European PatentApplication 91309239.1 and U.S. Pat. No. 4,099,692.

All of the above prepared membranes have nonuniform sized zeolitecrystals and are noncontinuous, exhibiting many voids. Obtainingfunctional zeolite membranes from low alkaline synthesis routes isdifficult because the heterogeneous crystals in the membrane require anenormous membrane thickness to seal pinholes and void structures whichlower the membrane selectivity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an electron micrograph showing a cross-sectional view of azeolite layer grown on the inverted face of a porous α aluminasubstrate.

FIG. 2 is an electron micrograph of a top view of a zeolite layer grownon the inverted face of a porous α alumina substrate.

FIG. 3 is an X-ray diffraction pattern showing the preferred orientationof a composition of the invention. The x-axis is 2 theta and the y-axisis intensity in CPS.

FIG. 4 is a schematic view of a zeolite layer on a porous substrate. (A)is the porous substrate, (B) the zeolite layer, (C) a grain boundary,(W) the width at one point along a zeolite crystal, and (T) thethickness of one crystal.

SUMMARY OF THE INVENTION

Applicant has discovered a new composition of matter containing zeoliteand a process for preparing the same. The composition is unique in thatthe zeolite crystals making up part of the composition pack in a mannersuch that the zeolite forms a layer which is essentially continuous withno large scale voids even when the zeolite layer is <10 μm thick.

Hence, one aspect of the present invention is directed toward acomposition of matter comprised of a substrate (also referred to hereinas a support) and a polycrystalline layer of zeolite crystals wherein atleast 99% of said zeolite crystals have at least one point betweenadjacent zeolite crystals that is <20 Å and wherein at least 90% of saidzeolite crystals have widths of from about 0.2 to about 100 microns andwherein at least 75% of said zeolite crystals have a thickness of within20% of the average crystal thickness. Preferably, the zeolite layer willhave at most 1 Volume % voids and the zeolite crystal will range fromabout 2 to about 50 microns.

Another aspect of the present invention is directed toward a process ofmaking the instant composition comprising the steps of:

(a) contacting a substrate with a zeolite synthesis mixture;

(b) hydrothermally treating said substrate and said zeolite synthesismixture for a time and at a temperature sufficient to form a zeolitelayer on said substrate and wherein settling on to said zeolite layer ofparticles produced from said zeolite synthesis mixture is prevented;

(c) removing any unreacted zeolite synthesis mixture.

Contacting as used herein includes total and partial immersion.

The process further comprises calcining said composition of step (c) ata temperature of about 400 to about 600° C. for at least about 10minutes when said zeolite synthesis mixture contains an organictemplate.

The compositions thus produced are useful, for example, for sizeexclusion separations such as separation of dye molecules from alcoholand oligomer separation from hexane.

Additionally, the compositions described herein are often referred to aszeolite membranes in the art and can be used as such.

Detailed Description of the Invention

Applicant has discovered a new composition comprising a polycrystallinezeolite layer on a support. The support can be porous or non-porous,preferably porous supports will be used. The zeolite layer can be grownon any porous supports including but not limited to alumina, titania,cordierite, zeolite, mullite, stainless steel, pyrex, silica, siliconcarbide, silicon nitride, carbon, graphite and mixtures thereof.Additionally, non-porous supports will include quartz, silicon, glass,borosilicate glasses, dense ceramnics, i.e., clays, metals, polymers,graphite and mixtures thereof When non-porous supports are utilized, thecompositions are useful as sensors or catalysts. Most preferably, thesupport will be a porous ceramic or porous metal.

Growth of the zeolite layer may be carried out by contacting thesubstrate in a zeolite synthesis mixture for a time and at a temperaturesufficient to effect crystallization. Hydrothermally treating may, forexample, in an autoclave under autogenous pressure. Contacting of thesubstrate must be carried out such that there is no settling of crystalsformed in the synthesis mixture during autoclaving onto the substrate.The synthesis mixture may thus be handled in a manner to prevent suchsettling.

In a preferred embodiment, the zeolite layer is grown on a support whichis inverted in the zeolite synthesis mixture. Inverted as used hereinmeans that the zeolite layer is grown on the side of the substrateoriented from 90 to 270 degrees in the synthesis mixture. In the 180degree orientation, the side of the substrate onto which the zeolitelayer is grown, is horizontal and facing downward. This is referred toas inverted. Preferably, the membrane will be grown on the 180 degreeoriented side. In the inverted orientation, the surface of the substrateto be coated should be at least 5 mm, from the bottom and sides of thevessel containing the zeolite synthesis mixture, preferably at least 8mm at its lowest point during the process of preparation. Applicantbelieves that inversion of the substrate prevents zeolite crystals,which are homogeneously nucleated in the zeolite synthesis mixture, fromsettling onto the substrate where the zeolite layer is grown. Thus, thecrystals do not incorporate into the growing zeolite layer or perturbthe growth process. Hence, at least 99%, preferably at least 99.9% ofthe crystals in the zeolite layer have at least one point betweenadjacent zeolite crystals that is ≦20 Å. In the instant invention, thespacing between adjacent crystals is set by a grain boundary zone andthe maximum grain boundary zone, absent voids or defects, will be ≦40 Å.Additionally, at least 90%, preferably at least 95% of the zeolitecrystals in the zeolite layer have widths of from about 0.2 to 100microns, preferably 2 to about 50 microns. As used herein, grainboundary zone is the width of the disordered zone between two adjacentordered crystals. The zeolite crystals in the zeolite layer areintergrown in the membrane so that nonselective permeation paths throughthe membrane are blocked by the narrowest point of approach betweencrystals. Nonselective permeation pathways are taken to be permeationpathways which exist at room temperature that do not pass through thezeolite crystals. This blockage of non-permeation pathways exists atroom temperature after a template which occludes the pore structure isremoved from the zeolite crystals. Templates which are used to grow thezeolite are often removed by a calcination step. From transmissionelectron microscopy (TEM) the narrowest point of approach betweencrystals of less than 20 Å after the template is removed is established.The space between crystals at this point can contain inorganic oxidematerial that restricts non-selective permeation of molecules throughthe membrane. The absence of non-selective permeation paths can bedetected by the ability to prevent the permeation at room temperature(˜20° C.) of dye molecules through the membrane after any template isremoved from the pore structure. Dye molecules which can be chosen todetect non-selective permeation pathways through the membrane shouldhave minimum dimensions which are larger than the controlling aperturethrough the zeolite and the size of the dye molecule should also be lessthan 20 Å. Non-selective pathways transport dye molecules which arelarger than the pore size of the zeolite. the dye molecules should becarried in a solution made with a solvent which can be transportedthrough the zeolite pore structure and the zeolite layer should not beallowed to pick up foreign contaminants (such as water) before beingtested. It is found that the compositions made in accordance with thepresent invention block the permeation of dye molecules at roomtemperature through the zeolite layer. All of the dye molecules chosenhave sizes less than 20 Å. The lack of permeation at room temperature ofdye molecules with sizes less than ˜20 Å demonstrates that non-selectivepermeation pathways with sizes less than ˜20 Å are blocked. It should benoted that this test does not have to be performed with a dye moleculeand any molecular species that can be detected having a size less than20 Å and greater than the zeolite pore dimension can be used. Theadvantage of using a dye molecule is that it can be readily detected byoptical means.

The habitus of MFI zeolite compositions grown in accordance with theinstant invention preferably display a degree of C-orientation (within30° of the normal to the surface of the substrate in the zeolite layer).More especially, the longest edges (thickness) of at least 75% of thecrystals are within 30° of perpendicular to the layer plane,advantageously at least 90% of the crystals being within that angle.

A measure of the crystallographic preferred direction of the unit celland of the proportion of the crystals that have the longest axis(thickness) normal to the plane of the layer may be obtained bycomparison of the X-ray diffraction pattern of the layer with that of arandomly oriented zeolite powder. In the case of an MFI-type zeolitewith predominant C-axis orientation, for example, the longest edgecorresponding to the c axis, the ratio of the intensity of the 002-peakto the combined 200 and 020 peak is divided by the same ratio forrandomly oriented powder; the quotient is termed the crystallographicpreferred orientation (CPO). Measured in this way, zeolite layers inaccordance with the invention have a CPO of at least 1, and may have aCPO as high as 500. The crystals in the zeolite layer range in thicknessfrom about 2 to about 100μ, preferably about 5 to 100μ, more preferablyabout 30 to about 60μ, most preferably about 30μ. Although the crystalsmay range in thickness from 2 to 100μ, for any given membrane, 75 Volume%, preferably 90 Volume % of the crystals will all have the crystalthicknesses of within 20% of the average crystal thickness. Thickness isherein defined as the length of the crystals from the substrate surfaceto the uppermost edge of the zeolite crystal perpendicular to thesubstrate. Compositions made from zeolites other than MFI will alsodisplay a degree of orientation in habitus and/or of the unit cell,however, such orientation may not be in the c direction. For example, A,B, and C orientations are possible, as well as mixtures thereof Otherorientations are also possible depending on the zeolite selected.

The instant compositions are virtually free of voids. They preferablyexhibit at most about 1 Volume % voids, preferably less than 0.5 Volume% voids.

Void as used herein means spaces between the zeolite crystals in thezeolite layer along grain boundaries larger than 40 Å. Defects arespaces between adjacent zeolite crystals extending through the thicknessof the zeolite layer. In the instant membrane, the total number ofdefects in the zeolite layer with sizes >40 Å is <10,000 per squareinch, preferably <100 per square inch. the number of defects havingspacing between adjacent zeolite crystals larger than about 2000 Å is<100/inch², preferably <0.1/inch². Voids and defects can be detectedfrom cross-sectional images of the zeolite layer made in the scanning ortransmission electron microscope. In the most preferable case, thezeolite layer will be substantially free of voids and defects.

Defects of the type described can be detected in dye permeationexperiments. Isolated points at which dye permeates into the substratereveal such defects. Defects can also be determined by examiningcross-sections of the zeolites membrane in the scanning electronmicroscope. Gas permeation can also be used to reveal defects in themembrane. If the permeability of the zeolite layer to nitrogen at roomtemperature is less than 5×10⁻⁶ moles/(m² -sec-Pascal) for each micronof thickness of the zeolite layer, the membrane can be considered tohave an acceptable defect density. More preferably, the permeability ofthe zeolite layer to nitrogen at room temperature is less than 5×10⁻⁷moles/m² -sec-Pascal) for each micron of thickness of the zeolite layer.The zeolite membranes of the instant invention are prepared from zeolitesynthesis mixtures. Zeolite synthesis mixtures are any mixtures fromwhich zeolite crystals are grown and are well known in the art. (See,e.g., Handbook of Molecular Sieves, Rosemary Szostak, Van NostrandReinhold, N.Y., 1992 and Zeolite Molecular Sieves, D. W. Breck, R. E.Kreiger Publishing Co., Malabar, Fla., 1984, ISBN 0-89874-648-5). Forexample, for MFI zeolites, the synthesis mixture can be a mixture havinga pH of about 8 to about 12 and is readily prepared by those skilled inthe art. For example, suitable mixtures include NA₂ O, TPABr(tetrapropyl ammonium bromide), SiO₂ and water. The membranes are grownby contacting the support material of choice in the zeolite synthesismixture. The synthesis mixture is then heated to about 50 to about 300°C., preferably about 100 to about 250° C., preferably about 180° C. fora period of about 30 minutes to about 300 hours. Any undesired growth onthe substrate can be easily removed by known techniques. For example,grinding can be used. Undesired growth does not refer to the zeolitelayer of the invention, but refers to growth on other surfaces of thesubstrate.

The zeolite layer compositions which can be prepared in accordance withthe instant invention include silicates, aluminosilicates,aluminophosphates, silicoalumino-phosphates, metalloaluminophosphates,stanosilicates and mixtures thereof Representative examples of suchzeolites are MFI, FAU (including zeolite x, zeolite y), zeolite beta,MAZ, LTA, LTL, CHA, AFI, AEL, BEA, EUO, FER, KFI, MOR, MEL, MTW, OFF,TON, AFS, AFY, APC, APD, MTN, MTT, AEL and mixtures thereof, preferablyMFI zeolite with a silicon to aluminum ratio greater than 30 will beused including compositions with no aluminum. MFI zeolites with Si/Alratios greater than 30 are herein referred to as silicalite.

Some of the above materials while not being true zeolites are frequentlyreferred to in the literature as such, and this term will be used hereinto include such materials.

The zeolite layer can have either a shape preferred orientation, acrystallographically preferred orientation, or both. Shape orcrystallographically preferred orientations occur because of the controlof the relative rates of nucleation and growth offered by the synthesisprocedure. Specifically, during synthesis, the rate of growth can bemade to dominate the rate of surface nucleation of new crystals orincorporation of new crystals. Incorporation of new crystals is definedas attachment onto the surface of the growing zeolite layer of a crystalformed in the synthesis mixture. Since the growth rate can dominaterenucleation or incorporation, crystals can competitively grow for longperiods of time without significant addition of new crystals into thegrowing layer. Since the growing layer is composed of individualcrystals and the synthesis method seeks to prevent renucleation orincorporation of crystals, the resulting composition can have shape,crystallographically preferred orientation, or both. Shape orientationoccurs because the crystals grow with preferred regular habits (ormorphology) at the surface of the zeolite layer. A regular habit (ormorphology) is taken to be a regularly shaped outline of a particularcrystallographic grain in the layer. Regularly shaped outlines aredefined as those which can be fitted or packed together so that thereare no interconnected spaces or voids between crystals. Interconnectedvoids will form a pore structure. A few examples of regular habits withregular shapes are columnar, cubic, rectangular, and prismatic.Spherical, irregular and elliptical shapes are not considered to beregular habits. In a shape preferred orientational, defined layers willhave the same regular habit. This can be measured by cleaving orfracturing the substrate on which the layer is grown and examining thecross-sectional morphology of the zeolite layer with a scanning electronmicroscope. Examining the surface of the as grown zeolite layer can alsogive additional information concerning the shape preferred orientationin the layer. A layer with shape preferred orientation is taken to beone which has more than 90% of the crystals within one layer inside thezeolite layer exhibiting self similar regular habits. The self similarrequirement means that the same regular habit is exhibited within alayer that can be drawn in the electron micrograph of the cross-sectionof the zeolite layer, however, even though the shapes are the same, theydo not all have to be the same size. Because of the growth mechanism ofthe zeolite layer, it is possible to have one shape preferredorientation at the bottom (base) of the layer and another shapepreferred orientation in a layer drawn near the surface. An example ofthis is an MFI zeolite layer which has a columnar habit at the base ofthe layer and a rectangular habit at the surface of the layer. Many MFIzeolite layers grown in accordance with the present invention exhibitonly one habit throughout the thickness of the zeolite layer. UsuallyMFI zeolite layers grown in accordance with the present inventionexhibit only one habit throughout the thickness of the zeolite layer.Usually MFI zeolite layers with a preferred C-axis orientation exhibit acolumnar habit (or morphology) throughout the entire thickness of thezeolite layer. Often shape preferred orientational layers have apreferred crystallographic orientation.

The substrate on which the zeolite layer is grown may be porous ornon-porous. If the substrate is porous, it will be a porous materialthroughout its entire thickness. Preferably an inorganic oxide orstainless steel will be utilized. The porous substrate, hence can be aceramic, metal, carbide, polymer or mixture thereof. The poroussubstrate, hence may have a uniform pore size throughout or may beasymmetrical, having a larger pore structure throughout the bulk of thesubstrate with a smaller pore structure at the surface on which thezeolite layer is to be grown. The substrate pore size is dictated bymass transfer considerations. It is preferred that the pore structureand thickness of the substrate be chosen such that the mass transferresistance does not limit the flux of material permeating through thezeolite membrane during use. The porous substrate will hence display aporosity of about 5 to about 70%, preferably about 20 to about 50% andan average pore size of about 0.004 to about 100μ, preferably about t0.05 to about 2 microns.

It is preferred that the surface of the substrate, porous or non-porous,on which the zeolite layer is grown be smooth. Roughness in thesubstrate leads to defects in the zeolite layer. The substrate shouldhave an average roughness with an amplitude of less than 10 μm with anaspect ratio of the roughness less than 1:1. It is preferable that theaverage roughness of the substrate be less than 0.5 μm with an aspectratio of the roughness less than 1:1. Though non-porous substrates maybe utilized, porous substrates are preferred.

Once the zeolite layer has been grown, the substrate, with attachedzeolite layer may preferably be washed with water for a time and at atemperature sufficient to remove any zeolite synthesis mixture which didnot react during hydrothermal treatment. Hence, washing may be conductedat a temperature of about 15 to 100° C., preferably about 80 to about100° C., for at least 10 minutes, preferably at least six hours. Excesswashing for longer periods will not affect the compositions separationcapabilities. Additionally, any liquids or solutions capable of removingthe excess zeolite synthesis mixture may be used.

Once washed, if the zeolite synthesis mixture contained an organictemplate, the composition is calcined at about 400 to 600° C. for atleast one hour, preferably at least about six hours. Longer calcinationtimes will not affect the performance of the membrane.

The compositions are useful for separation processes whereby feedstockderived from petroleum, natural gas, hydrocarbons, or air comprising atleast two molecular species is contacted with the composition of theinvention and at least one molecular species of said feedstock isseparated from said feedstock by said composition and wherein saidhydrocarbon feedstocks are coal, bitumen and kerogen derived feedstocks.

Specifically, the following table shows some possible feedstocks derivedfrom petroleum, natural gas, air, or hydrocarbons and the molecularspecies separated therefrom by use of the instant compositions. Thetable is not meant to be limiting.

    ______________________________________                          Separated    Feedstock             Molecular Species    ______________________________________    Mixed xylenes (ortho, para, meta) and                          Paraxylene    ethylbenzene    Mixture of hydrogen, H.sub.2 S, and ammonia                          Hydrogen    Mixture of normal and isobutanes                          Normal butane    Mixture of normal and isobutenes                          Normal butene    Kerosene containing C.sub.9 to C.sub.18 normal paraffins                          C.sub.9 to C.sub.18 normal                          paraffins    Mixture of nitrogen and oxygen                          Nitrogen (or oxygen)    Mixture of hydrogen and methane                          Hydrogen    Mixture of hydrogen, ethane, and ethylene                          Hydrogen and/or                          ethylene    Coker naphtha containing C.sub.5 to C.sub.10 normal                          C.sub.5 to C.sub.10 normal olefins    olefins and paraffins and paraffins    Methane and ethane mixtures containing argon,                          Helium, neon, and/or    helium, neon, or nitrogen                          argon    Intermediate reactor catalytic reformer products                          Hydrogen, and/or light    containing hydrogen and/or light gases                          gases (C.sub.1 -C.sub.7)    Fluid Catalytic Cracking products containing                          Hydrogen, and/or light    H.sub.2 and/or light gases                          gases    Naphtha containing C.sub.5 to C.sub.10 normal paraffins                          C.sub.5 to C.sub.10 normal                          paraffins    Light coker gas oil containing C.sub.9 to C.sub.18 normal                          C.sub.9 to C.sub.18 normal    olefins and paraffins olefins and paraffins    Mixture of normal and isopentanes                          Normal pentane    Mixture of normal and isopentenes                          Normal pentene    Mixture of ammonia, hydrogen, and nitrogen                          Hydrogen and nitrogen    Mixture of A10 (10 carbon) aromatics                          e.g. Paradiethylbenzene                          (PDEB)    Mixed butenes         n-butenes    Sulfur and/or nitrogen compounds                          H.sub.2 S and/or NH.sub.3    Mixtures containing Benzene (Toluene)                          Benzene    H.sub.2, propane, propylene                          Hydrogen and/or                          propylene    ______________________________________

Applicants believe that molecular diffusion is responsible for the aboveseparations. Additionally, the compositions can be used to effect achemical reaction to yield at least one reaction product by contactingthe feedstocks as described above or below with the compositions havinga catalyst incorporated within the zeolite layer, or support, or byplacing the catalyst in close enough proximity with the composition toform a module. A module would react the feedstock just prior to itsentrance into the composition or just after its exit from thecomposition. In this manner one can separate at least one reactionproduct or reactant from the feedstocks. The catalysts of choice forparticular process fluids are well known to those skilled in the art andare readily incorporated into the instant compositions or formed intomodules with the compositions by one skilled in the art. The followingtable represents some of the possible feedstocks/processes, in additionto those above which can be reacted and some possible products yielded.The table is not meant to be limiting.

    ______________________________________    Feedstock/process  Product Yielded    ______________________________________    Mixed xylenes (para, ortho, meta) and                       Paraxylene and/or ethylbenzene    ethylbenzene    Ethane dehydrogenation to ethylene                       Hydrogen and/or ethylene    Ethylbenzene dehydrogenation to                       Hydrogen    styrene    Butanes dehydrogenation butenes                       Hydrogen    (iso's and normals)    Propane dehydrogenation to                       Hydrogen and/or propylene    propylene    C.sub.10 -C.sub.18 normal paraffin                       Hydrogen    dehydrogenation to olefins    Hydrogen Sulfide decomposition                       Hydrogen    Reforming          Hydrogen, light hydrocarbons    dehydrogenation/aromatization                       (C.sub.1 -C.sub.7)    Light Petroleum Gas                       Hydrogen    dehydrogenation/aromatization    Mixed Butenes      n-butenes    ______________________________________

The supported zeolite layer of the invention may be employed in suchseparations without the problem of being damaged by contact with thematerials to be separated. Furthermore, many of these separations arecarried out at elevated temperatures, as high as 500° C., and it is anadvantage of the supported layer of the present invention that it may beused at such elevated temperatures.

Further separations which may be carried out using the composition inaccordance with the invention include, for example, separation of normalalkanes from co-boiling hydrocarbons, for example normal alkanes fromiso alkanes such as C₄ to C₆ mixtures and n-C₁₀ to C₁₆ alkanes fromkerosene; separation of aromatic compounds from one another, especiallyseparation of C₈ aromatic isomers from each other, more especiallypara-xylene from a mixture of xylenes and, optionally, ethylbenzene, andseparation of aromatics of different carbon numbers, for example,mixtures of benzene, toluene, and mixed C₈ aromatics; separation ofaromatic compounds from aliphatic compounds, especially aromaticmolecules with from 6 to 8 carbon atoms from C₅ to C₁₀ (naphtha range)aliphatics; separation of olefinic compounds from saturated compounds,especially light alkenes from alkane/alkene mixtures, more especiallyethene from ethane and propene from propane; removing hydrogen fromhydrogen-containing streams, especially from light refinery andpetrochemical gas streams, more especially from C₂ and lightercomponents; and alcohols from aqueous streams; alcohols from otherhydrocarbons particularly alkanes and alkenes that May be present inmixtures formed during the manufacture of alcohols and separation ofheteroatomic compounds from hydrocarbons such as alcohols and sulphurcontaining materials such as H₂ S and mercaptans.

The present invention accordingly also provides a process for theseparation of a fluid mixture which comprises contacting the mixturewith one face of a layer according to the invention under conditionssuch that at least one component of the mixture has a different steadystate permeability through the layer from that of another component andrecovering a component or mixture of components from the other face ofthe layer.

The invention further provides a process for catalysing a chemicalreaction which comprises contacting a feedstock with a layer accordingto the invention which is in active catalytic form under catalyticconversion conditions and recovering a composition comprising at leastone conversion product, advantageously in a concentration differing fromits equilibrium concentration in the reaction mixture. For example, ap-xylene rich mixture from the reactor or reactor product in a xylenesisomerization process; aromatic compounds from aliphatics and hydrogenin a reforming reactor; hydrogen removal from refinery and chemicalsprocesses such as alkane dehydrogenation in the formation of alkenes,light alkane/alkene dehydrocyclization in the formation of aromatics(e.g., Cyclar), ethylbenzene dehydrogenation to styrene. The inventionfurther provides a process for catalysing a chemical reaction whichcomprises contacting one reactant of a bimolecular reaction with oneface of a layer according to the invention, that is in the form of amembrane and in active catalytic form, under catalytic conversionconditions, and controlling the addition of a second reactant bydiffusion from the opposite face of the layer in order to more preciselycontrol reaction conditions. Examples include controlling ethylene,propylene or hydrogen addition to benzene in the formation ofethylbenzene, cumene or cyclohexane, respectively.

The invention further contemplates separation of a feedstock asdescribed herein wherein the separated species reacts as it leaves thecomposition or as it passes through the composition and thus formsanother product. This is believed to increase the driving force fordiffusion through the zeolite layer.

Catalytic functions can be incorporated into the instant compositions.When a catalytic function is incorporated into the composition, it canbe used as an active element in a reactor. Several different reactorarchitectures can be constructed depending on the location of thecatalytic site in the composition. In one case the catalytic functioncan be located within the zeolite layer, while in another case thecatalytic function can be located within the support, and in anothercase the catalytic function can be distributed throughout the supportand the zeolite layer. In addition, catalytic function can beincorporated into a reactor by locating conventional catalyst particlesnear one or more surfaces of the composition such that specific productsor reactants are continuously and selectively removed or added to thereaction zone throughout the reactor. Impregnating with catalyticallyactive metals such as Group VIII noble metals, e.g. Pt, can impart thecatalytic function to the composition. The catalytically active metalscan be incorporated by techniques known in the art such as incipientwetness. The amount of Group VIII noble metal to be incorporated willrange from about 0.01 to about 10 wt %.

Some specific reaction systems where these compositions would beadvantageous for selective separation either in the reactor or onreactor effluent include: selective removal of a para-xylene richmixture from the reactor, reactor product, reactor feed or otherlocations in a xylenes isomerization process; selective separation ofaromatics fractions or specific aromatics molecule rich streams fromcatalytic reforming or other aromatics generation processes such aslight alkane and alkene dehydrocyclization processes (e.g., C₃ -C₇paraffins to aromatics from processes such as Cyclar), methanol togasoline and catalytic cracking processes; selective separation ofbenzene rich fractions from refinery and chemical plant streams andprocesses; selective separation of olefins or specific olefin fractionsfrom refinery and chemicals processing units including catalytic andthermal cracking, olefins isomerization processes, methanol to olefinsprocesses, naphtha to olefins conversion processes, alkanedehydrogenation processes such as propane dehydrogenation to propylene;selective removal of hydrogen from refinery and chemicals streams andprocesses such as catalytic reforming, alkane dehydrogenation, catalyticcracking, thermal cracking, light alkane/alkene dehydrocyclization,ethylbenzene dehydrogenation, paraffin dehydrogenation; selectiveseparation of molecular isomers in processes such as butaneisomerization, paraffin isomerization, olefin isomerization, selectiveseparation of alcohols from aqueous streams and/or other hydrocarbons.

The following examples are for illustration and are not meant to belimiting.

EXAMPLES

1. Materials

The hydrothermal experiments were performed using mixtures of thefollowing reagents: NaOH (Baker), Al (NO₃)₃, 9H₂ O(Baker), LudoxAS-40(Dupont), tetrapropylammonium bromide (98%, Aldrich), and distilledwater.

Porous alumina and stainless steel substrates were used for the supportof the zeolite layers. The average pore size and porosity of the aluminasubstrate was about 800 Å and 32%, respectively. Porous sinteredstainless steel substrates from Mott's (0.25 μm) and Pall (M020, 2 μm)were obtained. All of the substrates were cleaned with acetone in anultra-sonic bath, dried at 120° C. and then cooled down to roomtemperature before use.

2. Hydrothermal Reaction

MFI membranes were prepared from two different reaction batch mixtures,one contained silica only to make high silica MFI and the other withadded alumina to make ZSM-5. they have the general formulation x M₂ 0:10Si0₂ :z Al₂ 0₃ :pTPABr:y H₂ 0; M can be NA, K, Rb, & Cs, x varied from0.1 to 0.15 and p varied from 0.2 to 1. All the results shown in thenext section have the composition of 0.22 Na₂ 0:10 Si0₂ :0Al₂ 0₃ :280 H₂0:0.5 TPABr (tetrapropylammoniumbromide) with the exception of the ZSM-5sample which contained 0.05 Al₂ 0₃. the 1.74 g or TPABr and 0.45 g ofNaOH (50 wt %) were dissolved in 52 ml of distilled water with stirring.To this solution, 18.8 g of Ludox AS-40 was then added with agitationfor at least 15 minutes until a uniform solution was formed.

The substrates were placed inverted (180 degree orientation) in a Teflonlined reaction vessel supported on a stainless steel wire frame. Thedistance between the substrate and the bottom of reactor was at least 5mm. The synthesis solution was then poured into the reactor to cover thewhole substrate. The autoclave was sealed and placed in an oven, whichpreheated at the desired temperature. The reaction bombs were removedfrom the oven after reaction and cooled to room temperature. The coatedsubstrates were washed with hot water for at least 6 hours, thencalcined at 500° C. for 6 hours in air. The heating rate was controlledat 10° C./hour.

3. Analysis

The resulting membranes were characterized by x-ray diffraction,electron microscopy and permeability measurement.

Results and Discussion

1. Products

The following table shows some typical examples synthesized underdifferent experimental conditions, such as reaction time, and substrate.

                                      TABLE 1    __________________________________________________________________________                             Reaction                                  Zeolite Layer                                         C-axis    Sample        @ Substrate              Pore Size μm                    Reaction Temp °C.                             Time Hrs                                  Thickness μm                                         Result    __________________________________________________________________________    1   alumina              0 08  180       4    4     CPO MFI    2   alumina              0 08  180       8   12     CPO MFI    3   alumina              0 08  180      18   30     CPO MFI    4   SS    0 25  180       4    4     CPO MFI    5   SS    0 25  180       8   11     CPO MFI    6   SS    0 25  180      20   30     CPO MFI    7   alumina              0 08  158      64   45     CPO MFI    8   alumina              1 0   158      64   45-50  CPO MFI    9   SS    0 25  158      64   50     CPO MFI    10  SS    2 0   158      64   50     CPO MFI    __________________________________________________________________________     @ alumina: 0.08 μm and 1 μm pore size;     SS = stanless steel, Pall Corporation, PMM Grade M020 (2 μm) and Mott     Corp (0 25)     CPO  Crysallographic Preferred Orientation

What is claimed is:
 1. A method for preparing a composition comprisingthe steps of:(a) contacting a substrate with a zeolite synthesismixture; (b) hydrothermally treating the substrate and the zeolitesynthesis mixture for a time and at a temperature sufficient to form azeolite layer on said substrate wherein settling of particles producedfrom said zeolite synthesis mixture, during treatment, onto said zeolitelayer is prevented, the zeolite layer being a polycrystalline zeolitelayer of zeolite crystals wherein at least 99% of the zeolite crystalshave at least one point between adjacent crystals that is less than orequal to 20 Å, wherein at least 90% of the zeolite crystals have widthsof about 0.2 to about 100 microns, and wherein at least 75% of thezeolite crystals have a thickness within 20% of the average crystalthickness; and (c) removing any unreacted zeolite synthesis mixture. 2.A method according to claim 1 wherein said composition is calcined at atemperature of 400 to 600° C. for at least 30 minutes when said zeolitesynthesis mixture contains an organic template.
 3. A method according toclaim 1 wherein said substrate is oriented such that said zeolite layeris grown on the side of the substrate oriented from 90 to 270 degreesrelative to the surface of the synthesis mixture, and wherein in the 180degree orientation, the zeolite layer is grown on the horizontaldownward facing side.
 4. A separation process comprising contacting afeedstock derived from petroleum, natural gas, air or hydrocarbons,comprising at least two molecular species with a composition comprisinga substrate and a layer of polycrystalline zeolite crystals wherein atleast 99% of said zeolite crystals have at least one point betweenadjacent crystals that is ≦20 Å and wherein at least 90% of saidcrystals have widths of from about 0.2 to about 100 microns and whereinat least 75% of said crystals have a thickness within 20% of the averagecrystal thickness wherein at least one molecular species of saidfeedstock is separated from said feedstock by said composition, andwherein said hydrocarbon feedstocks are selected from the groupconsisting of coal, bitumen, kerogen and mixtures thereof.
 5. A processaccording to claim 4 wherein said molecular species is separated viamolecular diffusion.
 6. A process according to claim 4 wherein saidfeedstock is selected from the group consisting of mixed xylenes andethylbenzene; hydrogen, H₂₅ and ammonia; mixtures of normal andisobutanes; mixtures of normal and isobutenes; kerosene containingnormal paraffins; mixtures of nitrogen and oxygen; mixtures of hydrogenand methane; mixtures of hydrogen, ethane and ethylene; mixtures ofhydrogen, propane and propylene; coker naphtha containing C₅ to C₁₀normal olefins and paraffins; methane and ethane mixtures containingargon, helium, neon or nitrogen; intermediate reactor catalytic reformerproducts; fluid catalytic cracking products; naphtha; light coker gasoil; mixtures of normal and isopentanes; mixtures of normal andisopentenes; mixtures of ammonia, hydrogen and nitrogen; mixtures of C₁₀aromatics; mixtures of butenes; mixtures of sulfur and nitrogencompounds; mixtures of sulfur compounds; mixtures of nitrogen compounds;and mixtures thereof.
 7. A process according to claim 4 wherein saidcomposition adsorbs at least one molecular species of said feedstock. 8.A process for catalyzing a chemical reaction comprising contacting areaction stream under catalytic conversion conditions with a compositioncomprising a substrate and a polycrystalline layer of zeolite crystalswherein at least 99% of said zeolite crystals have at least one pointbetween adjacent crystals that is ≦20 Å and wherein at least 90% of saidcrystals have widths of from about 0.2 to about 100 microns and whereinat least 75% of said crystals have a thickness within 20% of the averagecrystal thickness.
 9. A process according to claim 8 wherein a catalystforms a module with said composition or is contained within saidcomposition.
 10. A process according to claim 9 wherein said feedstockis selected from the group consisting of mixed xylenes and ethylbenzene;ethane; ethylbenzene; butanes; propane; C₁₀ -C₁₈ normal paraffins; H₂ S;catalytic reforming streams; light petroleum gases (LPGs); sulfur andhydrogen compounds; nitrogen compounds; mixed butenes, and mixturesthereof.
 11. A process according to claim 10 wherein when said feedstockis reacted with said composition a reactant or reaction product isobtained.
 12. A process for catalyzing a chemical reaction whichcomprises contacting one reactant of a bimolecular reaction mixture withone face of a composition comprising a substrate and a polycrystallinelayer of zeolite crystals wherein at least 99% of said zeolite crystalshave at least one point between adjacent crystals that is ≦20 Å andwherein at least 90% of said crystals have widths of from about 0.2 toabout 100 microns and wherein at least 75% of said crystals have athickness within 20% of the average crystal thickness that is in activecatalytic form, under catalytic conversion conditions, and controllingthe addition of a second reactant by diffusion from the opposite face ofthe structure, thereby catalyzing the chemical reaction between saidreactants.